As dj_paige said, Adobe never announces future release dates. However, we can make educated guesses based on past data. LR 6 has been averaging 53 days between releases supporting new cameras. Adding 53 days to the release date of LR CC 2015.5.1 (4/28/16) yields 6/20/16.

In the past, 86% of new Panasonic cameras have been supported by LR in the first release after the camera's official announcement. Since the GX85 was announced on 4/5/16, three weeks before CC 2015.5.1, it appears very likely it will be supported in 2015.6, whenever it comes out.

All of which is still a guess ... and I don't think it's fair or reasonable to include the 2015.5.1 update in the average time between updates, it appears to have been pushed out ahead of any normal schedule to fix a serious bug; but maybe it is reasonable to include it in the average, no one really knows, and we're back to total guessing, aren't we?

I count any release that includes support for new cameras; here are the releases for CC 2015:

Release

Days since previous release

Number of cameras

6.1

55

6

6.1.1

44

16

6.2

68

4

6.3

43

6

6.4

71

8

6.5

49

13

6.5.1

43

3

Compare 6.5.1 (43 days, 3 cameras) with 6.1.1 (44 days, 16 cameras) or 6.3 (43 days, 6 cameras). For the purposes of predicting a future release of camera support based on past performance, it's hard to argue that 6.5.1 should be excluded while 6.1.1 included.

The data is consistent enough that you can make much better than wild guesses -- enough to put reasonable odds (and money) against. But there's enough variance in the data that I wouldn't put too much money :-> Especially considering the vagaries of product development...